共查询到20条相似文献,搜索用时 125 毫秒
1.
M. J. Perricone J. N. Dupont T. D. Anderson C. V. Robino J. R. Michael 《Metallurgical and Materials Transactions A》2011,42(3):700-716
A series of 31 Mo-bearing stainless steel compositions with Mo contents ranging from 0 to 10 wt pct and exhibiting primary
δ-ferrite solidification were analyzed over a range of laser welding conditions to evaluate the effect of composition and cooling
rate on the solid-state transformation to γ-austenite. Alloys exhibiting this microstructural development sequence are of particular interest to the welding community
because of their reduced susceptibility to solidification cracking and the potential reduction of microsegregation (which
can affect corrosion resistance), all while harnessing the high toughness of γ-austenite. Alloys were created using the arc button melting process, and laser welds were prepared on each alloy at constant
power and travel speeds ranging from 4.2 to 42 mm/s. The cooling rates of these processes were estimated to range from 10 K
(°C)/s for arc buttons to 105 K (°C)/s for the fastest laser welds. No shift in solidification mode from primary δ-ferrite to primary γ-austenite was observed in the range of compositions or welding conditions studied. Metastable microstructural features were
observed in many laser weld fusion zones, as well as a massive transformation from δ-ferrite to γ-austenite. Evidence of epitaxial massive growth without nucleation was also found when intercellular γ-austenite was already present from a solidification reaction. The resulting single-phase γ-austenite in both cases exhibited a homogenous distribution of Mo, Cr, Ni, and Fe at nominal levels. 相似文献
2.
T.D. ANDERSON J.N. DuPONT M.J. PERRICONE A.R. MARDER 《Metallurgical and Materials Transactions A》2007,38(1):86-99
The good corrosion resistance of superaustenitic stainless steel (SASS) alloys has been shown to be a direct consequence of
high concentrations of Mo, which can have a significant effect on the microstructural development of welds in these alloys.
In this research, the microstructural development of welds in the Fe-Ni-Cr-Mo system was analyzed over a wide variety of Cr/Ni
ratios and Mo contents. The system was first simulated by construction of multicomponent phase diagrams using the CALPHAD
technique. Data from vertical sections of these diagrams are presented over a wide compositional range to produce diagrams
that can be used as a guide to understand the influence of composition on microstructural development. A large number of experimental
alloys were then prepared via arc-button melting for comparison with the diagrams. Each alloy was characterized using various microscopy techniques. The
expected δ-ferrite and γ-austenite phases were accompanied by martensite at low Cr/Ni ratios and by σ phase at high Mo contents. A total of 20 possible
phase transformation sequences are proposed, resulting in various amounts and morphologies of the γ, δ, σ, and martensite phases. The results were used to construct a map of expected phase transformation sequence and resultant
microstructure as a function of composition. The results of this work provide a working guideline for future base metal and
filler metal development of this class of materials.
An erratum to this article can be found at 相似文献
3.
Yasuhiro Maehara 《Metallurgical and Materials Transactions A》1991,22(5):1083-1091
Effects of prior thermomechanical treatments on the superplasticity of a 25 wt pct Cr-7 wt pct Ni-3 wt pct Mo-0.14 wt pct
N δ/γ duplex stainless steel have been studied by means of hot tensile testing with constant crosshead speeds. The objective
is to increase the strain rate suitable for superplasticity. The strain rate is found to be markedly increased by a special
prior treatment,i.e., solution treatment at temperatures in the δ single-phase region with subsequent heavy cold-rolling. In hot tensile tests
at 1273 K, elongations greater than 1000 and 300 pct were observed at initial strain rates (έ) of 10−3 to 10−1 s−1 and 1 x 100 s−1, respectively. The results for strain rates 〈10−1 s−1 can be explained in terms of a structural superplastic effect due to grain refinement. In the case of έ 〉 10−1 s−1, transformation superplastic effects due to γ-phase precipitation from the σ-ferrite matrix are also important, especially
in the early stages of deformation. In the equiaxedδ/γ microduplex structures during stable superplastic deformation, there exists a mixture of two different structures,i.e., dislocated and recovered/ recrystallized δ grains with a homogeneous dispersion of dislocation-free γ particles. This result
shows that dynamic recrystallization ofδ grains occurs locally and intermittently due to the dispersion of relatively hardγ particles. The apparent average grain growth rate during deformation is small compared to static grain growth, because grain
refinement due to dynamic recrystallization reduces the superplasticity-enhanced grain growth. 相似文献
4.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献
5.
In situ dynamic observation of the progress of a peritectic reaction and transformation of Fe-(0.14 pct C)- and Fe-(0.42 pct C)-peritectic
Fe-C alloys has been successfully made with a combination of a confocal scanning laser microscope and an infrared image furnace.
The peritectic reaction is characterized by the formation of the γ-austenite phase at the junction of the liquid and the grain boundary of δ-ferrite crystals and subsequent propagation of the three-phase point, liquid/γ/δ, along the liquid/δ boundary, whereas the peritectic transformation occurs by the thickening of the intervening γ toward both the liquid side and the δ side. The rates of the peritectic reaction for the two peritectic alloys are found to be much faster than the rate that would
be controlled by carbon diffusion, suggesting that either massive transformation to γ or solidification as γ controls the rate. This is also the case for the Fe-0.14%C transformation in the hypoperitectic alloy. However, the rate
of the peritectic transformation in the Fe-0.42%C alloy is determined by carbon diffusion.
This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney,
Australia, under the joint sponsorship of ISS and TMS. 相似文献
6.
Dr. Stefan Heino 《Metallurgical and Materials Transactions A》2000,31(8):1893-1905
This study concerns the crystallographic identification and compositions of precipitates formed in superaustenitic stainless
steel. Three experimental alloys, all containing 24 wt pct Cr, 22 wt pct Ni, and 0.5 wt pct N but with varying amounts of
Mo and W, were investigated after sensitization heat treatment (aging) at 900 °C. The contents of Mo and W in the three alloys
were 7 wt pct Mo, (6 wt pct Mo + 2 wt pct W) and (5 wt pct Mo + 5 wt pct W), respectively. While σ and x were the main secondary phases found in the W-free alloy, replacement of Mo by W was found to promote the formation of Laves-related
phases with high Mo + W content. The complex crystallographic nature of Laves-related precipitates was exemplified through
the formation of intergrowing C14 Laves, μ, and C phases, all with closely related crystal structures. There was no difference in chemical composition between the three
phases. Prolonged aging resulted in intragranular precipitation of different intermetallic phases, as well as formation of
nitrogen bearing phases, π and Cr2N, adjacent to previously formed intermetallic precipitates. The content of Mo + W was found to decrease with increasing aging
time for all secondary phases. 相似文献
7.
Chuanyong Gui Akihiro Sato Yuefeng Gu Hiroshi Harada 《Metallurgical and Materials Transactions A》2005,36(11):2921-2927
We proposed a new method for developing Ni-base turbine disc alloy for application at temperatures above 700 °C by mixing
a Ni-base superalloy U720LI with a two-phase alloy Co-16.9 wt pct Ti in various contents. The microstructure and phase stability
of the alloys were analyzed using an optical microscope, a scanning electron microscope, energy-dispersive spectroscopy, and
an X-ray diffractometer. The yield strength was studied by compression tests at temperatures ranging from 25 °C to 1200 °C.
The results show that all the alloys had a dendritic structure. Ni3Ti (η) phase was formed in the interdendritic region in the alloys with the addition of Co-16.9 wt pct Ti, and its volume fraction
increased with the increase in the addition of Co-16.9 wt pct Ti. The results of exposure at 750 °C show that the addition
of Co-16.9 wt pct Ti to U720LI had a great effect on suppressing the formation of σ phase due to the reduced Cr content in the γ matrix. Compared to U720LI, the alloys with the addition of Co-16.9 wt pct Ti possessed higher yield strength. The solid-solution
strengthening of γ and γ′ and higher volume fraction of γ′ were assumed to cause this strength increase. 相似文献
8.
9.
John W. Elmer Joe Wong Thorsten Ressler 《Metallurgical and Materials Transactions A》2001,32(5):1175-1187
Phase transformations that occur in the heat-affected zone (HAZ) of gas tungsten arc welds in AISI 1005 carbon-manganese steel
were investigated using spatially resolved X-ray diffraction (SRXRD) at the Stanford Synchrotron Radiation Laboratory. In situ SRXRD experiments were performed to probe the phases present in the HAZ during welding of cylindrical steel bars. These real-time
observations of the phases present in the HAZ were used to construct a phase transformation map that identifies five principal
phase regions between the liquid weld pool and the unaffected base metal: (1) α-ferrite that is undergoing annealing, recrystallization, and/or grain growth at subcritical temperatures, (2) partially transformed
α-ferrite co-existing with γ-austenite at intercritical temperatures, (3) single-phase γ-austenite at austenitizing temperatures, (4) δ-ferrite at temperatures near the liquidus temperature, and (5) back transformed α-ferrite co-existing with residual austenite at subcritical temperatures behind the weld. The SRXRD experimental results were
combined with a heat flow model of the weld to investigate transformation kinetics under both positive and negative temperature
gradients in the HAZ. Results show that the transformation from ferrite to austenite on heating requires 3 seconds and 158°C
of superheat to attain completion under a heating rate of 102°C/s. The reverse transformation from austenite to ferrite on
cooling was shown to require 3.3 seconds at a cooling rate of 45 °C/s to transform the majority of the austenite back to ferrite;
however, some residual austenite was observed in the microstructure as far as 17 mm behind the weld. 相似文献
10.
In advanced 9 to 12 pct Cr steels, the Cr equivalent is used as a measure to check the formation of δ-ferrite. In the present analysis, 29 alloys of varying composition were vacuum induction melted, and the amounts of δ-ferrite were measured in as-tempered conditions. Based on this and previous results on 9 to 12 pct Cr steels, a new equation
for the Cr equivalent is proposed and correlated with the amount of δ-ferrite formation. Results indicate that the new Cr equivalent equation shows better correlation than previous equations
and predicts the amount of δ-ferrite formed reasonably well. 相似文献
11.
The coarsening of γ′ and the elevated-temperature hardness have been studied as a function of molybdenum content, time, and
temperature in experimental wrought nickel-base superalloys. The alloys were selected from a systematic series containing
3, 4 1/2, and 6 wt pct Al and 1 wt pct Al plus 3 1/2 wt pct Ti. Each of the aluminum (plus titanium) series consisted of four
alloys containing 0, 2, 5, and 8 wt pct Mo. The alloys were solution-treated plus aged up to 112 h at 1700°F (925°C) and up
to 1000 h at 1400°F (760°C). Molybdenum retards the coarsening of γ′ on aging; this retarding effect is most pronounced in
alloys containing 6 wt pct Al. The coarsening of γ′ particles follows Ostwald ripening kinetics. Hardness testingin vacuo at temperatures up to 1750°F (955°C) shows that molybdenum also increases the elevated-temperature hardness significantly.
The relation of elevated-temperature hardness to the volume fraction of γ′ is considered, and the influence of aluminum and
titanium contents is discussed. 相似文献
12.
Keith J. Leonard Joseph C. Mishurda Vijay K. Vasudevan 《Metallurgical and Materials Transactions B》2000,31(6):1305-1321
The solidification pathways, subsequent solid-state transformations, and the liquidus surface in the Nb-Ti-Al system have
been examined as part of a larger investigation of phase equilibria in Nb-Ti-Al intermetallic alloys. Fifteen alloys ranging
in composition from 15 to 40 at. pct Al, with Nb to Ti ratios of 4:1, 2:1, 1.5:1, 1:1, and 1:1.5, were prepared by arc melting
and the as-cast microstructures were characterized by optical microscopy (OM), microhardness, X-ray diffraction (XRD), differential
thermal analysis (DTA), backscattered electron imaging (BSEI), electron probe microanalysis (EPMA), and transmission electron
microscopy (TEM). The results indicate that the range of primary β solidification is much wider than that indicated in previously reported liquidus surfaces, both experimental and calculated.
Differential thermal analysis has identified the existence of a β to σ+γ transformation in three alloys where it was previously thought not to exist; confirmation was provided by high-temperature
vacuum heat treatments in the single-phase β region followed by rapid quenching. The location of the boundary between the β, σ, and δ primary solidification fields has been redefined. A massive β → δ transformation, which was observed in the cast microstructure of a Nb-25Ti-25Al alloy, was repeatable through cooling following
homogenization. A β → δ+σ eutectoid-like transformation in the 25 at. pct Al alloys, was detected by DTA and evaluated through microstructural analysis
of heat-treated samples. Trends in the β phase with variations in composition were established for both lattice parameters and microhardness. As a result of this
wider extent of the primary β solidification field, a greater possibility exists for microstructural control through thermal processing for alloys consisting
of either σ+γ, β+σ, or β+δ phases.
An erratum to this article is available at . 相似文献
13.
A melting and solidification study of alloy 625 总被引:1,自引:0,他引:1
M. J. Cieslak T. J. Headley A. D. Romig T. Kollie 《Metallurgical and Materials Transactions A》1988,19(9):2319-2331
The melting and solidification behavior of Alloy 625 has been investigated with differential thermal analysis (DTA) and electron
microscopy. A two-level full-factorial set of chemistries involving the elements Nb, C, and Si was studied. DTA results revealed
that all alloying additions decreased the liquidus and solidus temperatures and also increased the melting temperature range.
Terminal solidification reactions were observed in the Nb-bearing alloys. Solidification microstructures in gastungsten-arc
welds were characterized with transmission electron microscopy (TEM) techniques. All alloys solidified to an austenitic (γ)
matrix. The Nb-bearing alloys terminated solidification by forming various combinations of γ/MC(NbC), γ/Laves, and γ/M6C eutectic-like constituents. Carbon additions (0.035 wt pct) promoted the formation of the γ/MC(NbC) constituent at the expense
of the γ/Laves constituent. Silicon (0.4 wt pct) increased the formation of the yJLaves constituent and promoted formation
of the γ/M6C carbide constituent at low levels (<0.01 wt pct) of carbon. When both Si (0.4 wt pct) and C (0.035 wt pct) were present,
the γ/MC(NbC) and γ/Laves constituents were observed. Regression analysis was used to develop equations for the liquidus and
solidus temperatures as functions of alloy composition. Partial derivatives of these equations taken with respect to the alloying
variables (Nb, C, Si) yielded the liquidus and solidus slopes t(m
L
, m
S
) for these elements in the multicomponent system. Ratios of these liquidus to solidus slopes gave estimates of the distribution
coefficients (k) for these same elements in Alloy 625. 相似文献
14.
C. Y. Cui M. Osawa A. Sato Y. F. Gu D. H. Ping H. Harada 《Metallurgical and Materials Transactions A》2006,37(2):355-360
The effects of Ru additions on the microstructure and phase stability of the Ni-base superalloy U720LI were examined. The
results show that the alloys with Ru contents of 0 to 6 wt pct had a dendritic structure, and the volume fraction of the primary
γ solid-solution phase in the dendritic core increased with the increase in the Ru content. The Ru additions to U720LI had
little effect on suppressing the formation of the σ phase, because the elemental partitioning of Cr, Mo, and Co in the γ solid-solution
phase was not influenced by the Ru additions. However, the coarsening of the γ′ phase was restrained by the Ru additions in
the U720LI. 相似文献
15.
M. A. Neff B. A. Rickinson K. P. Young M. C. Flemings 《Metallurgical and Materials Transactions B》1978,9(4):469-476
A series of Ni-Nb-Al-Cr(γ/γ′- σ) alloys in the composition ranges Nb 19.3 to 23.2 wt pct, Al 2.5 to 5.2 wt pct and Cr 0 to 7.05 wt pct have been directionally
solidified under high thermal gradient (G) at both steady state and under conditions of abruptly or gradually changing growth
rate(ft). The critical ratio of G andR, (g/r)*, to achieve two-phase plane frontin- situ composite growth increases as chromium and niobium (Cb) concentration deviates from the trough or surface of two-fold saturation.
Interlamellar spacing of composites tend to decrease with increasing chromium content. Structures produced at steady state
growth in whichG/R < (G/R)* are consistent with previous work and can be related to the location of the alloy composition with respect to the line of
two-fold saturation. For alloys, which at lowG/R exhibited σ dendrites, any perturbation in growth velocity (atG/R > (G/R)*) precipitated a single phase σ (Ni3Nb) band. For alloys which at lowG/R exhibited γ dendrites a similar effect was achieved only when growth rate was reduced abruptly by more than an order of magnitude.
Interlamellar spacing of two alloys (approximately Ni-20 wt pct Nb-2.5 wt pct Al-6 wt pct Cr) was studied and for abrupt reductions
in growth rate in which bands were not produced, it was observed to decay slowly to the new steady state value over distances
which are inconsistent with the assumption of simple niobium diffusion control. A gradual increase in growth velocity for
one of these alloys resulted in extremely slow adjustment of interlamellar spacing occurring over a period greater than one
hour. An abrupt increase in growth velocity for all alloys caused immediate adjustment of interlamellar spacing to the new
steady state value.
M. A. NEFF formerly a Graduate Student, Mass. Institute of Technology
B. A. RICKINSON formerly Research Associate, Mass. Institute of Technology
K. P. YOUNG formerly Research Associate, Mass. Institute of Technology 相似文献
16.
The variation of the kinetics of the martensite transformation with carbon content and martensite habit plane has been investigated
in several Fe−Ni based alloys. Transformation in an Fe-25 wt pct Ni-0.02 wt pct C alloy exhibits predominantly athermal features,
but some apparently isothermal transformation also occurs. In a decarburized alloy, on the other hand, the observed kinetic
features, such as the dependence ofM
s
on cooling rate, were characteristic of an isothermal transformation. In contrast, Fe-29.6 wt pct Ni-10.7 wt pct Co alloys
with carbon contents of 0.009 wt pct C and 0.003 wt pct C transform by burst kinetics to {259}γ plate. At both these carbon levels, theM
b
temperatures of the Fe−Ni−Co alloys are independent of cooling rate. It is proposed that the change in kinetic behavior of
the Fe-25 pct Ni alloy with the different carbon contents is due to the occurrence of dynamic thermal stabilization in the
higher carbon alloy. Dynamic thermal stabilization is relatively unimportant in the Fe−Ni−Co alloys which transform by burst
kinetics to {259}γ plate martensite.
P. J. FISHER, formerly with the University of New South Wales
D. J. H. CORDEROY, formerly with the University of New South Wales 相似文献
17.
T. Khaled G. H. Narayanan S. M. Copley 《Metallurgical and Materials Transactions A》1978,9(12):1883-1890
The stability of theβ phase in the Ti-V, Ti-Mo, and Ti-V-Mo alloy systems was investi-gated, and theβ/α + β phase boundaries in these systems were determined in the range 300 to 600° C. The results indicate that Mo is more potent
than V in stabilizing theβ phase with respect to α phase formation and in retarding the β → α reaction kinetics. It is shown that increasing the oxygen
concentration in the alloys tends to enhance α phase formation in Mo-lean alloys (Mo contents < 15 wt pct), whereas it leads
to the formation of an oxide phase in Mo-rich alloys (Mo contents ≥15 wt pct).
Formerly Research Assistant, Department of Materials Science, University of Southern California 相似文献
18.
M. J. Cieslak J. J. Stephens M. J. Carr 《Metallurgical and Materials Transactions A》1988,19(3):657-667
The weldability and weld metal microstructure of Cabot Alloy 214 have been investigated with a variety of experimental and
analytical techniques. These include Varestraint hot crack testing, hot ductility testing, pulsed Nd:YAG laser welding, scanning
and analytical electron microscopy, electron microprobe analysis, and X-ray diffraction. A heat of Alloy 214 containing intentionally
alloyed B (0.003 wt pct) and Zr (0.07 wt pct) was much more sensitive to both fusion zone hot cracking as quantified by the
Varestraint test and to simulated heat-affected-zone (HAZ) cracking as quantified by hot ductility testing than a heat of
Alloy 214 containing no intentionally added B (0.0002 wt pct) or Zr (0.02 wt pct). Scanning electron microscopy of the high
B and Zr alloy showed the presence of dendritically-shaped, Zr-rich constituents in interdendritic regions in the gas-tungsten-arc
(GTA) welds. Electron microprobe analysis of these welds revealed a segregation pattern of Cr, Al, Mn, and Zr enrichment in
interdendritic regions and Ni and Fe enrichment in dendrite core regions. Analytical electron microscopy revealed the presence
of ZrX (X = B, C, N, O), M23C6, andγ′ in the fusion zone of GTA weld specimens,γ′ was also found in the as-received base metal and in the GTA weld HAZ. X-ray diffraction analysis of extractions from the
high B and Zr GTA weld metal also indicated the presence of a ZrX-type constituent. The results of this study are in qualitative
agreement with earlier work performed on alloys such as NIMONIC 90 and INCONEL 718∗ relative to the detrimental effect of B and Zr additions on fusion zone and HAZ hot cracking susceptibility.
Formerly with Sandia National Laboratories, Albuquerque, NM 相似文献
19.
Mengtao Xie Randolph Helmink Sammy Tin 《Metallurgical and Materials Transactions A》2012,43(4):1259-1267
In the current investigation, the effect of Cr on the solidification characteristics and as-cast microstructure of pseudobinary
γ-δ eutectic alloys based on a near-eutectic composition (Ni-5.5Al-13.5Nb at. pct) was investigated. It was found that Cr additions
promote the formation of a higher volume fraction of γ-δ eutectic microstructure in the interdendritic region. Increasing levels of Cr also triggered morphological changes in the
γ-δ eutectic and the formation of γ-γ′-δ ternary eutectic during the last stage of solidification. A detailed characterization of the as-cast alloys also revealed
that Cr additions suppressed the liquidus, solidus, and γ′ precipitation temperature of these γ/γ′-δ eutectic alloys. A comparison of the experimental results with thermodynamic calculations using the CompuTherm Pandat database
(CompuTherm LLC, Madison, WI) showed qualitative agreement. 相似文献
20.
Mahmoud M. Farag Roberto Matera Merton C. Flemings 《Metallurgical and Materials Transactions B》1979,10(3):381-388
γ/γ/’-δ eutectic alloy containing 21.5 wt pct Nb, 2.5 wt pct Al, balance Ni was directionally solidified under a thermal gradient
(G) of 500 K/cm and different schedules of growth rate (R). Under steady state growth rate conditions, the critical (G/R) for plane front solidification is 25 K h/cm2. At progressively lower (G/R) the structure becomes richer in γ-phase,i.e. hypoeutectic. Sudden increase in growth speed causes the structure to change from lamellar to cellular and gradual increase
in growth speed results in interlamellar spacings that are larger than the extremum values. Sudden decrease in growth speed
causes little disturbance in the structure but causes the eutectic grain size to increase. 相似文献